This invention relates to heat pipes. More particularly this invention relates to improvements to the evaporator section of a dual manifold evaporator with an intermediate bank of evaporator tubes.
A heat pipe is a device that transfers thermal energy by the evaporation and condensation of a working fluid that is enclosed in the evacuated heat pipe vessel. Heat from an external source is absorbed in the evaporator end of the heat pipe and acts to transform the working fluid from a liquid phase to a vapor phase. The vapor then travels to the condenser end of the heat pipe system where the vapor condenses and transfers energy to thermal equipment that is connected to the condenser. The condensed fluid then flows back to the evaporator section to begin the cycle again. The passage connecting the evaporator section to the condenser section is generally referred to as the vapor space or the adiabatic region. The working fluid is normally in a saturated state, enabling the heat pipe to operate at near uniform temperature.
To construct a compact heat pipe heat exchanger that can transfer a large quantity of energy from a distributed heat source, one solution is to use a bank of heat pipes in parallel. The individual heat pipes generally are not interconnected in these systems; the evaporator of one heat pipe leads only to the condenser of the same pipe. Such systems are used in some commercial air-to-air heat exchangers, and they have also been used in a few fuel-fired boiler systems.
In some situations, it is desirable to combine the heat input from several heat pipe evaporators and to deliver the energy to a single condenser region. In effect, such a system would collect energy from a distributed source and deliver the energy to a single destination. This has been accomplished in the past by combining the condenser ends of several heat pipes whose evaporator ends are in the hottest region of a boiler with the evaporator end of a single, larger capacity heat pipe whose condenser end passes the thermal energy to a thermal load. This method of linking heat pipes adds to the system's cost and complexity and increases the overall temperature drop through the system.
There have been a umber of attempts to combine a plurality of evaporator tubes directly with a single condenser to collect heat from a diffuse source and transfer it to a single point. None has been particularly successful due to a variety of design and performance shortcomings. The structures illustrated in FIGS. 7 and 8 of U.S. Pat. No. 3,977,364 to Gijsgers et al. for "Apparatus for Evaporating Fluids" are representative. This patent is incorporated by reference herein in its entirety. One problem in particular is caused by overflow of condensate from the upper manifold down the inner walls of the tubes which upsets the evaporation in these areas by quenching the operation of the affected tube and causing undesirable local overheating and temperature oscillations in the system.